Question

I have data like below: (columns Name1 and Name2) as a result of another query.

Name1 Name2

A B

B A

However, any such pairings should actually be considered just one, and should be only reported as A B (A comes before B , alphabetically sorted)

How do I do it in Oracle / PlSQL?

Answer 1

You could do something like this:

SELECT DISTINCT Name1, Name2
FROM (
      SELECT Name1, Name2 FROM t WHERE Name1 <= Name2
      UNION ALL
      SELECT Name2, Name1 FROM t WHERE Name1 > Name2
     );

Which should work and is quite simple, but is not as efficient as:

SELECT DISTINCT
       CASE WHEN Name1 <= Name2 THEN Name1 ELSE Name2 END AS Name1
      ,CASE WHEN Name1 <= Name2 THEN Name2 ELSE Name1 END AS Name2
FROM t;

or just:

SELECT DISTINCT
       LEAST(Name1, Name2) AS Name1
      ,GREATEST(Name1, Name2) AS Name2
FROM t;

I have not considered NULLs in these queries. You’d have to modify the <= comparisons to take these into account, if the columns are nullable.